Spark plug connectors define the electrical connection between a spark plug and an ignition voltage source and are pushed onto the connecting tip of a spark plug. A contact element of the spark plug connector establishes the connection between the center electrode of the spark plug and the ignition cable of the voltage source. The spark plug is usually for use in internal combustion engines. The electrode or electrodes project into the combustion chamber for the purpose of igniting the mixture.
Such a spark plug connector is disclosed in German patent publication 195 15 623. The housing of this spark plug connector is made of electrically insulating material and a contact element of electrically-conducting elastic material is mounted in this housing. A sleeve-shaped cable holder for the ignition cable is formed onto the housing of the spark plug connector. This cable holder includes an inwardly projecting cable connector which is in electrical connection with the contact element. The contact element is configured as a contact ring made of electrically-conducting elastic material such as silicon having a specific graphite content or an insert made of metal wires. The contact ring is held as an inserted component in a cylindrical recess of the housing. The housing itself is rigid. When the spark plug connector is pushed onto a spark plug, then the connecting tip of the spark plug penetrates the contact ring and widens the same. The restoring spring force of the expanded contact ring presses the inner surface of the contact ring against the connecting tip and ensures the electrical contact.
The elastic material of the contact ring makes possible only small spring deflections so that the restoring forces of the contact material are only adjustable with difficulty. Vibrations caused by the operation can lead to wear at the contact element whereby the contact force of the elastic ring can become scattered.
If a helical spring is used as a contact element in a spark plug connector, then the helical spring must be pressed axially upon the connecting tip of the spark plug. The helical spring too defines only short effective spring deflections so that large forces are required for pushing the spark plug connector onto the spark plug in order to ensure the required contact force of the helical spring. When disconnecting the insert connection, often very large pulling forces act on the helical spring which can lead to a permanent deformation and reduction of the spring action.